The Arduino Keyboard library: a board that types

// Stream deck on a Pro Micro: six keys, their labels on a 128x64 OLED, and a
// hotkey sent over USB for each press through Keyboard.h.
//
// The labels are the point. A plain macro pad makes you remember which key
// is which; here the screen shows a label over each key, the one you press
// lights up, and the sixth key flips to a second page of five more actions.
//
// Wiring.
//
//   keys      4 5 6 7 8 9 (each to GND, pulled up inside the chip)
//   OLED      SSD1306 on I2C: SDA pin 2, SCL pin 3, VCC 5 V, GND
//
// In Mokxi: click the arcade buttons. The OLED shows the page and lights the
// key you hold, and the Serial Monitor shows the hotkey the board would type.
//
// Hotkeys. Each action is Ctrl + Shift + an F-key from F13 to F22. Almost no
// program uses F13 and up on its own, so streaming and recording software
// (OBS Studio's hotkey settings, for one) can take them without clashing with
// anything. Press the key in the program's hotkey box once and it learns it.
//
// Not simulated: the USB connection to a PC. Mokxi models this chip's USB as
// a serial pipe, so each press prints as a [Keyboard] line on the Serial
// Monitor. Flash the same sketch to a real Pro Micro and it types the keys.

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <Keyboard.h>

// ---------------------------------------------------------------------------
// Make it yours
// ---------------------------------------------------------------------------

const uint8_t KEY_PINS[6] = {4, 5, 6, 7, 8, 9};

// Two pages of five actions; key 6 always turns the page. Labels are six
// characters at most so they fit a key's box.
const char *const LABELS[2][5] = {
    {"SCENE1", "SCENE2", "MUTE", "CAM", "REC"},
    {"BRB", "CLIP", "MARKER", "CHAT", "LIVE"},
};
const uint8_t HOTKEYS[2][5] = {
    {KEY_F13, KEY_F14, KEY_F15, KEY_F16, KEY_F17},
    {KEY_F18, KEY_F19, KEY_F20, KEY_F21, KEY_F22},
};
// Held with every hotkey. Change to just KEY_LEFT_CTRL, or add KEY_LEFT_ALT.
const uint8_t MODIFIERS[2] = {KEY_LEFT_CTRL, KEY_LEFT_SHIFT};

const unsigned long LOCK_MS = 20;  // debounce: ignore a key this long after a change

// ---------------------------------------------------------------------------

Adafruit_SSD1306 display(128, 64, &Wire, -1);

uint8_t page = 0;
bool held[6];
unsigned long changedAt[6];

void drawKey(uint8_t k) {
  int16_t x = (k % 3) * 43;
  int16_t y = 16 + (k / 3) * 24;
  bool lit = held[k];
  display.fillRect(x, y, 42, 22, lit ? SSD1306_WHITE : SSD1306_BLACK);
  display.drawRect(x, y, 42, 22, SSD1306_WHITE);
  display.setTextColor(lit ? SSD1306_BLACK : SSD1306_WHITE);
  display.setCursor(x + 3, y + 7);
  display.print(k == 5 ? "PAGE>" : LABELS[page][k]);
}

void draw() {
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(0, 2);
  display.print("STREAM DECK  page ");
  display.print(page + 1);
  for (uint8_t k = 0; k < 6; k++) {
    drawKey(k);
  }
  display.display();
}

void send(uint8_t k) {
  for (uint8_t m = 0; m < 2; m++) Keyboard.press(MODIFIERS[m]);
  Keyboard.press(HOTKEYS[page][k]);
  Keyboard.releaseAll();
  Serial.print("Key ");
  Serial.print(k + 1);
  Serial.print(": ");
  Serial.println(LABELS[page][k]);
}

void setup() {
  for (uint8_t k = 0; k < 6; k++) {
    pinMode(KEY_PINS[k], INPUT_PULLUP);
  }
  Serial.begin(115200);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  Wire.setClock(400000);  // fast mode: the screen redraws sooner
  Keyboard.begin();
  draw();
  Serial.println("Stream deck ready: page 1");
}

void loop() {
  unsigned long now = millis();
  bool redraw = false;
  for (uint8_t k = 0; k < 6; k++) {
    bool down = digitalRead(KEY_PINS[k]) == LOW;
    if (down == held[k] || now - changedAt[k] < LOCK_MS) {
      continue;
    }
    held[k] = down;
    changedAt[k] = now;
    redraw = true;
    if (!down) {
      continue;
    }
    if (k == 5) {
      page = (uint8_t)(1 - page);
      Serial.print("Page ");
      Serial.println(page + 1);
    } else {
      send(k);
    }
  }
  if (redraw) {
    draw();
  }
}